FIELD AND LABORATORY EXERCISES 135 



delivery pipes are supplied with numerous openings through 

 which the water flows upon the field. By turning the line of pipe 

 with a lever the direction of the small streams of water is changed 

 so that the water may be more conveniently and evenly distrib- 

 uted over the surface. The delivery pipes are close enough to- 

 gether so that the water from two parallel pipes may reach all of 

 the area between them. 



FIELD AND LABORATORY EXERCISES 



1. Make a farm level by securing two elbow joints of %-inch pipe on the 

 ends of a piece of %-inch pipe 2 feet long. When the elbows are securely on, 

 they should both point upward when the pipe is on the table. Then in the 

 upper openings of the two elbows insert a piece of glass tubing about % inch 

 in diameter and 4 inches long. This may be done with perforated rubber 

 corks or in some convenient method. Color some water with a little black 

 ink and fill the "level" until the water stands level half way up in the glass 

 tubes. This " level" is permanently level whenever it is resting on a table or 

 box in the field where it is being used. One may sight across the top of the 

 liquid in the two glasses and this line of sight will be in the level plane of opera- 

 tion in laying out drainage systems. 



2. Another device for use in running levels is made by driving two four- 

 penny finish nails in the two ends of a carpenter's level which is about 2 feet 

 or thirty inches in length. Have the nails stand at equal heights above the 

 wood. When the spirit in the level reads correctly, the operator may sight 

 across the top of the two nails, and this line of sight will be in the level plane. 

 Both of these devices are reasonably accurate for preliminary surveys. 



3. Make a sighting pole by selecting a large piece of wood about 1x2 inches 

 and 12 feet long. Carefully mark this off with a soft black pencil at intervals 

 of one foot. Number these by pasting on a prominent number above each of 

 the marks. The figures for this may be cut from a large calendar. This pole 

 may be held by the pole-man, who will carry a foot ruler in his hand for use in 

 determining the exact height of the pole where the line of sight of the instru- 

 ment-man strikes the pole. For longer distances the pole-man may point to 

 the line of sight with a pencil covered with a handkerchief and when the true 

 point on the pole has been found, the height above the nearest foot mark is 

 measured with a ruler and the reading recorded. 



4. Running Levels. -With the above instruments, students should prac- 

 tice running levels, taking the readings at intervals 100 feet apart along a road 

 or along other lines selected for practice. From the data thus obtained, make 

 drawings showing the amount of rise and fall along the surface of the ground, 

 indicating the distances at each point below a stated line above called the 

 datum line. 



5. The above exercise should be repeated in a field where drainage might 

 be worth considering. From the data obtained calculate the amount of fall 

 possible along the line of operation. It is safe to assume that the head or 

 upper end of the line of trial drainage should be two feet under the surface 

 of the ground, and should not come closer to the surface than that at any 

 point, except near the mouth, where the water is to empty. 



6. Outflow from Drains. If drain tiles are in use in the vicinity, the out- 

 lets should be examined at intervals of say every eight hours after a heavy 

 rainfall. The records should be taken each time/ Make notes of the gradual 

 increase and decrease in the outflow. What do these indicate with reference 

 to the efficiency of the drainage in that particular case? 



